1. Field of the Invention
The present invention relates to methods and apparatus for completing and maintaining subterranean wells for producing oil, gas and other fluids and minerals from the earth. In particular, the invention relates to a method and apparatus for setting a well annulus packer or bridge plug.
2. Description of Related Art
Packers and bridge plugs are devices for sealing the annulus of a borehole between a pipe string that is suspended within the borehole and the borehole wall (or casing wall). Hereafter, the term “packer” will be used as a generic reference to packers, bridge plugs or other such flow channel obstructions. The functional purpose of a packer is to obstruct the transfer of fluid and fluid pressure along the length of a flow channel such as a borehole.
Typically, inflatable packer assemblies utilize either mud, water or cement to inflate an elastomer (rubber) bladder from a tubular mandrel. The mandrel is a pipe joint in an assembly string of tubing suspended within a well bore. Inflation of the bladder seals it against a well bore or casing wall to obstruct the annulus continuity between the well wall and tubing string. Inflatable packers expanded by mud or water typically utilize a valve system to maintain fluid pressure in the packer bladder. Cement systems, on the other hand, generally rely on the compressive strength of the cured or hardened cement. Both systems have inherent deficiencies.
A packer that is inflated with mud or water is dependent solely on the reliability of the valve that confines the fluid pressure charge. Leakage of the valve results in deflation of the packer and loss of the annulus seal. Characteristically, cement is compounded as a pumpable non-heterogeneous liquid. Over a relatively short working time, free water in the compound is captured (cured) to alter the compound phase from liquid to solid. Accordingly, liquid phase cement is needed to inflate this packer bladder. After a curing time of a few hours, sufficient compressive strength to support significant weight above the packer. Considering the fact that the packer setting event occurs under the control and direction of a rig crew and that rig expenses are in the tens of thousands of dollars per hour, the time devoted to cement curing is enormously expensive.
For a truly long-term or permanent packer, traditional wisdom will hold for the inflating fluid to be solid within the bladder to prevent leakage over time and to resist thermal effects which are generally more dramatic in fluids than in most solids. Consequently, the bladder of permanent packers is most often inflated by cement. The time lapse after mixing phase change from liquid to solid for cement may be controlled to some degree, by formulation. However, temperature and well fluid contamination may sometimes uncontrollably influence the phase change interval.
Moreover, a significant caveat to the use of a cement inflated packer is the consequence of an error in positioning the packer. If erroneously set within a well fluid production zone, there is great potential for irreparable well damage. Accidental spillage within the wellbore is also a major concern. Use of cement inflated packers, therefore, carries a high risk element.
U.S. Pat. No. 5,488,994 describes a fluid phase change system for setting a packer wherein the packer bladder is inflated by a polymer resin. As the resin is pumped into the bladder expansion voids, the resin flow is channeled over and mixed with a catalyst material. An in situ phase change of the resin occurs within the bladder voids as a consequence of the catalyst chemical reaction. Similar to cement set packers, the resin that inflates the packer bladder as a liquid, reacts into a solid to permanently secure the inflated profile.
An object of the present invention, therefore is provision of a phase changing inflation system for well packers that is neither time nor temperature dependent for changing from a liquid phase to inflate the packer to a solid phase to secure the packer.
Another object of the invention is an inflation system for well packers in which a liquid that is pumped down a tubing or pipe string flow bore is not stimulated to a phase change until actually entering a packer inflation chamber.
A further object of the invention is an inflation system for well packers in which only liquid that actually enters a packer inflation chamber is stimulated to a phase change.
Also an object of the invention is reduction, if not elimination, of uncertainties associated with actual bottom hole temperatures the heat generated within a packer inflation fluid as it is being pumped into a well and the time required to complete the operations.